Manufacture of phenols



I No Drawing.

Patented Oct. '18, 1932 UNITED. STATES PATENT OFFICE WILLIAM J. HALE AND EDGAR C. BRITTON, OF MIDLAND, MICHIGAN, ASSIG'IN'ORS TO THE DOW 'CHEMICALGOMPANY, OF .MIDLAND, .MICHIGAN, A CORPORATION OF MICHIGAN MANUFACTURE OF PHENOLS The present invention relates to the manu facture of phenols by means of the hydrolysis of the corresponding halogen substituted aromatic hydrocarbons, and more particular: ly to hydrolysis of such halogenated aromatlc hydrocarbons through the agency of a salt of a strong base and a weak acid in aqueous solution, 1

The present application is a continuation 1 in part of our copending application filed June 26, 1923, Serial No. 647,898.-

The object of our invention is to'provide a process of the aforesaid nature whereby free phenols are pro uced directly as distinguished from existing commercial processes wherein the alkaline salts of phenols, or phenates, are the immediate product; such phenates requiring to be treated further with an acid in order to liberate the phenols as such. Another object is to secure greater economy of raw materials entering into the process and consequently a lower cost of manufacture. Other objects and advantages will appear as hereinafter described.

To the accomplishment ofthe foregoing and relatedends, the invention, then, consists of the steps hereinafter fully described and particularly pointed out in the claims, the following description setting forth but a few of the various ways in which the principle of the invention may be'used.

It is Well known that chlorbenzene can be hydrolyzed by dilute (10 to 20 per cent) aqueous solutions of caustic alkali by heating under pressure at temperatures up to 300 C. The basis of this method is set forth in detail by Meyer and Bergius (Berichte 47 3155-3160, 1914) Taking as an example the production of phenol from chlorbenzene, the course of the reaction is given by the two equations;

lllorbenzene Phenol (3) CuHrON a+CoHsCl-)CuHsO CaHs-l-N 8C1 diphenyl oxide Application filed m a, 1929. Serial No. 375,873.

The diphenyl oxide so produced is then hydrated slowly to phenate atthe reaction temperature of about 300 (3., if a" sufficiently large excess of caustic alkali solution is present;

The product obtained by this method is sodium phenate which must be'treated with an acid to liberate free phenol, such method thusinvolving an extra step as wellas the added expense of the acid. To secure a high yield of phenate, an excess of at least 2 moles NaOH is required over and above the 2 moles thereof theoretically'called for according to equations (1). and (2). Such excess, of course, is lost when the reaction mass is acidulated and also necessitates the use of a correspondingly greater quality of acid for neutralization. Consequently, for each mole of phenol produced, approximately 4 inoles of caustic soda and 3 moles of hydrochloric or other equivalent acid are consumed.

Following the method outlined above, Meyer and Bergius obtained a 96 per cent yield of phenol as phenate when they used 4 moles of NaOH,-to one mole of chlorben zene but with a smaller proportional amount of caustic soda the yield was appreciably diminished and diphenyl oxide was formed in correspondingly larger amount. While with caustic alkali a smooth substitution of Clby a high yield, they under pressure at 300 C. for 8 hours with sodium carbonate solution, and a like meager yield was obtained with borax solution in 9 hours at 297 C.

To summarize, the present processes for the production of phenols by the hydrolysis of halogenated aromatic hydrocarbons with aqueous caustic alkalis do not yield a phenol directly, but a phenate; a large excess of alkali is necessary to convert the diphenyl oxide formed to phenate, and an amount of acid equivalent to all of the alkali used is required for as an intermediate product back decomposing the phenate and neutralizing the excess of alkali. Processes employing weaker alkalis have returned but a small yield of phenol experimentally, and heretofore have not been capable of successful commercial application.

In contradistinction to the published results of Meyer & Bergius (loc. cit.), we have now discovered that it is possible under appropriate conditions to obtain directly a high yield of free phenol, as distinguished from phenate, by replacing caustic alkali as hydrolytic agent with certain basic salts, which may be generally described as salts of a strong base and a weak acid, examples of which are the borates, carbonates, silicates and phosphates of thealkali metals.

Such basic saltsjn aqueous solution are slightly hydrolyzed by the action of water, a condition of equilibrium being set up, as illustrated in the following equations;

droxide is normally very low but neverthes less it is sufiicient to efiect the exchangeof hydroxyl for halogen in halogen substituted aromatic hydrocarbons when the latter are heated under pressure with an aqueous solution of one of the above basic salts at temperatures, in the case of chlorinated derivatives, for example, between 300 and 400 0.

During the progress of the reactiona very large excess of halogenated hydrocarbon, as compared with alkali hydroxide formed by hydrolysis, is always present in the mixture.

Such hydroxide, therefore, is completely con- 7 sumed in the production of the phenol, and

neutralizing the phenol so produced to form, phenate. The supply of alkali hydroxide is constantly replenished at about. the same rate as it is consumed by of basic salt. i v

The reactions between a halogenated aromatic hydrocarbonfe. g., chlorbenzene, and

further, hydrolysis basic salts of the character herein described are expressed in the following equations;

In the course of the reaction the basic salt is converted into the corresponding acid salt .in equimolecular proportion to the phenol formed. -In Equation (8) the unstablesodium acid borate breaks down furtherinto amore stable, metaborate and metaboric acid.

The reaction mixture on standing) forms twodistinct layersreadily separable y mechanical means, one containing mostof the phenol and the other an aqueous solution "of the inorganic salts together with a little phenol.

The phenol layer may be purified in the usual way, as by distillation; the aqueous salt solution may be distilled with steam toseparate the small amount of phenol dissolved therein and then regenerated simply by adding caustic alkali to convert the acid salt back to the basic salt, viz;

(11) NaHCO5+ NaOH Na COQ 4: H O

transformedto acid salt from which the former is regenerated by adding alkali. Such regenerated basic salt is then reused, so that the total amount of basic salt in circulation under continuous operation remains practically constant. Only one molecular equivalent of caustic alkali for each equivalent of phenol produced is required for regenerating the basic salt solution, whereas in other processes from two to four equivalents of alkali to one of phenol are consumed. Further, in our'improved process no acid is required for neutralization. Thus important economies in the consumption of raw materials are effected. 1

The efi'ective reacting temperatures depend in the first place upon the particular halogen substituent of the ar'omatic hydrocarbon, brom-substituted derivatives, of course, being more readily hydrolyzed than the corresponding chlor-derivatives. With the former temperatures as low as 250 C. may be suflicient, whereas with the latter commercial yields are obtained, as previously stated,'at temperatures between 300 and 400 C. In practice we have found it advantageous to employ temperatures materially above 300 (3., e. g. from 320 to 390 C., but above about 410 0., decomposition becomes appreciable.

Ewample 1 A mixture consisting of 1 mole chlorbenzene and 1.2 mole borax in approximately 10 per cent aqueous solution is placed in an autoclave andheated under pressurefor 40 minutes at an average temperature of 370 C. The reaction product, after cooling and discharging trom the autoclave, is allowed to separate into two' layers, one containing free phenol and the other being an aqueous salt solution containing a little phenpl. dissolved therein. The phenol layer is distilled in the 3 usual way for the separation of diphenyl oxide and unreact'ed chlorbenzene and the preparation of a purified phenol product. The aqueous layer is boiled to "steam off its content of phenol, which is separately recovered, and then is treated with caustic soda in amount sufficient to regenerate the basic salt, whereupon the solution may be employed for a succeeding reaction. Yield of phenol is approximately 56 per cent, and of diphenyl oxide 13 per cent, based upon the chlorbenzene used. The excess of unreacted chlorbenzene is recovered and may be returned to a later reaction. L

A mixture containing 1 mole chlorbenzene and 1.2 mole of an approximately 14 per cent solution of sodium carbonate is heated under pressure at about 370 C. for 1% hours. The reaction product is worked up in similar manner as described in Example 1. Yield of phenol is approximately 60 per cent, and of diphenyl oxide 17 per cent.

The above described improved process is applicable generally to the production of phenols and substituted derivatives thereof by the hydrolysis of the corresponding mono or poly-halogen substituted aromatic hydrocarbons as well as derivatives of such halogenated hydrocarbons containing other nonhydrolyzables substituent groups. For example, the mono-halogenated toluenes may be converted to the corresponding cresols, dihalogenated benzenes to the corresponding di hydroxy phenols, halogenated naphthalenes to the corresponding naphthols, halogenated diphenyls to hydroxy-diphenyls, etc.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the process herein disclosed, provided the step or steps stated by any of the following claims, or the equivalent of such stated step or steps be employed.

We therefore particularly point out anddistinctly .claim our invention 1. The process of making a free phenol directly without acidification of the reaction product which comprises heating a halogenated aromatic hydrocarbon with an aqueous solution of a basic salt included in the group of the borates, carbonates, phosphates and silicates of the alkali metals under pressure at a temperature between 320 and 400 C.

2. The process of making a free phenol directly without acidification of the reaction product which comprises heating a halogenated aromatic hydrocarbon with an aqueous solution of a basic salt included in the group of the borates, carbonates, phosphates and silicates of the alkali metals under pressure at a temperature between 320 and 400 (3., separating the phenol formed from the residual aqueous solution, regenerating the basic salt in the latter by adding caustic alkali and returning such solution to the initial reaction.

3. The process of making a free phenol directly without acidification of the reaction product which comprises heating a chlorinated aromatic hydrocarbon with an aqueous solution of a basic salt included in the group,

of the borates, carbonates, phosphates and silicates of the alkali metals under pressure at a temperature between 320 and 400 C.

4. The process of making a free phenol directly without acidification of the reaction product which comprises heating a chlorinated aromatic hydrocarbon with an aqueous solution of a basic salt included in the group of the. borates, silicates ofthe alkali metals under pressure at a temperature between 320 and 400 (3., separating the phenol formed from the residual aqueous solution, regenerating the basic salt in the latter by adding caustic alkali and returning such solution to the initial reaction.

5. The process of making free phenol directly without acidification of the reaction product which comprises reacting chlorbenzene'and an aqueous solution of a basic salt included in the group of the borates, carbonates, phosphates and silicates of the alkali metals under pressure at a temperature between 320 and 400 C. and a corresponding pressure.

6. The process of making free phenol directly without acidification of the reaction product Which comprises reacting chlorbenzene and an aqueous solution of a basic salt included in the .group of the borates, carcarbonates, phosphates and bonates, phosphates and silicates of the alkali metals under pressure at a temperature between 320 and 400 C. and a corresponding pressure, separating phenol from the residual aqueous solution, regenerating the basic salt in the latter by adding caustic alkali and returning such solution to the initial reaction.

7. The process of making free phenol directly without acidification of the reaction product which comprises reacting chlorbenzene and an aqueous sodium carbonate solution at a temperature between 320 and 400 C. and a corresponding pressure.

8] The process of making free phenol di- 2 rectly without acidification of the reaction product which comprises reacting chlorbenzene and an aqueous sodium carbonate solution at a temperature between 320 and 400 C. and a corresponding pressure, separating phenol from the residual aqueous solution, regenerating the basic salt in the latter by adding caustic soda and returning such solution to the initial reaction. I

9. The process of making a phenol which comprises reacting a halogenated aromatic hydrocarbon with an aqueous solution of a basic salt from the group consisting of the borates, carbonates, phosphats and silicates of the alkali-metals by heating under pressureat a temperature between 320 and 400 C.,.whereby. the free phenol instead of a phenate is formed in the reaction mixture, and separating such phenol by mechanical means without acidifying the reaction product.

10. The process of making a phenol which comprises reacting a chlorinated aromatic hydrocarbon with an aqueous solution of a basic salt from the group consisting of the borates, carbonates, phosphates and silicates of the alkali-metals by heating under pressure at a temperature between 320 and 400 (1., whereby the free phenol instead of a phenate is formed in the reaction mixture, and separating such phenol by mechanical means without acidifying the reaction product.

a 11. The process of making phenol which comprises reacting chlorobenzene with an aqueous solution of a basic salt included within the group consisting of the boratcs, carbonates, phosphates and silicates of the alkali-metals by hcatingnnder pressure at a temperature between 320 and 400 0.,

' whereby free phenol instead'of an alkalirnetal phenate is formed in the reaction mixture, and separating said phenol by mechanical means without acidifying the reaction. product.

12. The process of making phenol which comprises reacting chlorobenzene with an aqueous sodium carbonate solution by heating under pressure at a temperature between 320 and 400 (1, whereby free phenol instead of the sodium phenate is formed in the reaction mixture, and separating said phenol by mechanical means Without acidifying the reaction product.

Signed by us, this 28 day of June, 1929.

:WILLIAM J. HALE. EDGAR C. BRITTON. 

